The pyroelectric effect is observed when a pyroelectric material is subjected to a change in temperature. By way of example, a thin, parallel-sided sample of material, such as a tourmaline crystal can be cut so that its crystallographic symmetry axis is perpendicular to the flat surfaces. The unit cells of pyroelectric materials so cut have a net dipole moment oriented along the direction normal to the flat surfaces (or along the crystallographic symmetry axis). The dipole moment per unit volume of the material is called the spontaneous polarization PS. PS is always nonzero in a pyroelectric material. PS exists in the absence of an applied electric field and can be thought of as a layer of bound charge on each flat surface of the sample, one face having a net positive charge and the other a net negative charge.
Present applications of the pyroelectric effect include infrared detectors, the production and manipulation of focused and unfocused electron and ion beams under vacuum conditions, x-ray generation and x-ray fluorescence measurements, and possibly the induction of nuclear reactions. Aside from a report by Sato et al., Chem. Lett. 2005, 34, 1178-1179, of laser desorption of ions from lead lanthanum zirconate titanate (PLZT), to the best knowledge of the inventors, pyroelectric materials have not previously been employed as a source of ions for chemical analysis using mass spectrometry.
There is a need for a compact, robust, ambient pressure ion source that can be used in mass spectrometry.